The present invention relates to a material having antioxidant properties, and to a process for preparing such material.
Artificial antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary-butylhydroxyquinone (TBHQ) and propyl gallate (PG) are known. However, in recent years, there has developed a movement towards avoiding using artificial additives, particularly where foodstuffs and medicaments are concerned. Much effort has therefore been invested in obtaining antioxidants from plants and especially from the Labiatae plant family.
Thus, in U.S. Pat. No. 3,950,266 (Chang et al.), there is described a process for extracting antioxidant material from rosemary or sage, using organic solvents boiling at up to 100xc2x0 C. (examples of which are hexane, benzene, ethyl ether, chloroform, ethylene dichloride, dioxane and methanol) and subsequently carrying out various steps of purification. It appears that in all practical examples, before further purification, the crude antioxidant was washed with water, and then bleached with active carbon. It will be appreciated that antioxidant material produced in this manner will be solvent-soluble and water-insoluble.
By contrast, according to U.S. Pat. No. 4,012,531 (Viani), extraction of plant material is carried out in absence of organic solvents, under mildly alkaline conditions, using a basic aqueous buffer at pH from 7 to about 11.5, preferably in an inert atmosphere. Examples describe the extraction of rosemary, sage and parsley at pH 8.6-9.3, at 55-90xc2x0 C.
In U.S. Pat. No. 4,450,097 (Nakatani et al.), antioxidant material is isolated from rosemary by extraction with a non-polar solvent, removal of the solvent and steam distillation, giving an aqueous dispersion, which was filtered, antioxidant being obtained from the solid material by further processing including extraction with aq. alkali at pH at least 10.5. An isolated antioxidant is 7xcex2,11,12-trihydroxy-6,10-(epoxymethano)abieta-8,11,13-trien-20-one.
U.S. Pat. No. 4,638,095 (Chang et al.) describes the isolation from rosemary of the antioxidant xe2x80x9crosmaridiphenolxe2x80x9d, which is structurally a dibenzocycloheptene derivative. This compound was obtained by chromatographic separation (and appeared in the 75:25 diethyl ether/hexane fraction) of a product made by a procedure including solvent extraction and steam distillation.
U.S. Pat. No. 4,877,635 (Todd) describes a process for producing an oil-soluble extract of a Labiatae herb claimed to contain essentially all of the antioxidant substances in the herb, in the course of which acetone- or methyl ethyl ketone-insolubles, defined as pro-oxidant substances, are, so far as practicable, removed by precipitation. U.S. Pat. No. 5,023,017 (Todd) relates to a stable Labiatae antioxidant solution, having a pH 8.4-11.8, prepared from an initial solvent extract of the herb, and claimed to contain (besides less than 75% water, and an edible alcohol and/or polyol) essentially all of the antioxidant substances in the herb, which is preferably rosemary, sage or thyme.
U.S. Pat. No. 5,433,949 (Kahleyss et al.), after referring to U.S. Pat. No. 5,017,397 which describes preparation of antioxidants by extracting Labiatae species with CO2 at 350-1000 bar and subsequent fractionation, proposes to prepare antioxidants from a similar source by a multistep process utilizing extraction with CO2 at 80-300 bar, treating the extraction residue with a C1-4 alcohol or C5-7 hydrocarbon followed by active carbon, and washing out the resultant solvent extract with water to remove color, aromatics and remaining solvent.
It is evident that the various methods known to the prior art for obtaining antioxidants from plants of the Labiatae family have for the most part been based on the assumption that the desired materials are to be found in water-insoluble extracts obtained by extracting with non-aqueous solvents, particularly water-immiscible solvents, and in many of the relevant patents, aqueous fractions are rejected. Moreover, in Todd ""635, acetone-insolubles are removed, being considered to contain undesired pro-oxidants, and in Todd ""017 it is again emphasized that the acetone insoluble materials do not contain antioxidants. Although, as has been noted above, the Viani patent describes direct extraction of the plants with buffered aqueous alkali; the product on evaporation gives a mixture of the desired product with inorganic materials, separation from which entails at least a further step involving crystallization, ion-exchange treatment or acidification. Moreover, the present inventor has found that the product precipitated on acidification on Viani""s alkaline solution is essentially water-insoluble.
In U.S. Pat. No. 4,354,035 (Christ et al.), there is described a process for isolating rosmarinic acid (of formula depicted below) from essentially water-immiscible organic solvent extracts of an aqueous extract made by extracting Melissa 
officinalis with water at 80-100xc2x0 C., and acidifying to pH 2-2.5. This patent does not suggest that an industrially useful water-soluble product could be made directly from aqueous extracts of Melissa officinalis, without requiring use of water-immiscible organic solvent extracts.
According to the Christ et al. patent, rosmarinic acid is valuable in view of its antiinflammatory properties, see e.g. U.S. Pat. No. 4,329,361 (Zenk et al.). However, rosmarinic acid is also known for its use in skin-treatment or cosmetic compositions, see e.g. JP 63162611 and U.S. Pat. No. 5,393,526 (Castro). Moreover, rosmarinic acid is claimed to be useful in a composition for protection against erythema and inflammatory reactions caused by exposure to UV rays, and to have antioxidant, antibacterial and antifungal activity, see FR 2652001. The action of rosmarinic acid as a 5-lipoxygenase inhibitor is also featured in JP 1121217, where, extracted from perilla species, it is used as a constituent of an antiallergic food. Moreover, in FR 2652001, rosmarinic acid is used in a composition for protection against erythema and inflammatory reactions caused by exposure to UV rays, and is said to have antioxidant, antibacterial and antifungal activity. In FR 2652001, rosmarinic acid is extracted from powdered plants (after defatting and depigmenting by petroleum ether extraction) with 80% (aq.) alcohol and eluting with water on a cellulose column. Although Viani mentions rosmarinic acid, camosic acid and pro-oxidant flavones, as extracted from rosemary at pH 8.5, there was no inference in this or other prior art, that the plants contained an extractable rosmarinic acid salt, or that this acid (or its derivatives) could per se be viable for antioxidant applications, i.e. to inhibit oxidation of other substances.
Mention is also made of the Albeck et al. and Grossman et al. patents (see U.S. Pat. Nos. 4,857,325, 4,923,697, 4,986,985, 4,997,666 and 5,124,167), which relate to the preparation of antioxidants by aqueous extraction of plant material specifying certain plant families and species, and utilization of such antioxidants. These patents neither disclose nor suggest that antioxidants might be obtained by similarly extracting plants of the Labiatae family, nor do they identify the chemical structure of the antioxidants.
The entire contents of the above-mentioned U.S. Patents are incorporated herein by reference.
Contrary to what is to be expected from the prior art, it has surprisingly been found by the present inventor that useful water-soluble and acetone-insoluble antioxidant material may be obtained from plants of the Labiatae family by extraction, which may be carried out at ambient temperatures, with aqueous extractant, by a process in which use of buffered alkali and a step of separation from admixed salts, need not arise.
It is thus an object of the present invention to provide a process for direct extraction of water-soluble antioxidant material from the plants in question, wherein plant material is extracted using weakly acidic, neutral or alkaline aqueous extractant.
It is a further object of the present invention to provide material which is highly efficient in terms of antioxidant activity, as compared with many known antioxidants used in industry.
Also, in view of much of the prior art on this subject, the inventor has unexpectedly found that conventionally rejected aqueous residues from the plant material in question, which has already been solvent extracted to remove water-insoluble solutes (including antioxidants such as carnosic acid), may nevertheless be used in the present process and afford in this manner useful antioxidant material. Thus, it is yet a further object of the present invention to provide a process for extraction of water-soluble antioxidant material from aqueous residues of known extraction processes wherein plants of the Labiatae family have already been subjected to extraction to remove water-insoluble solutes.
Another object of the invention is to provide a process permitting maximum recovery of industrially useful components from plants of the Labiatae family, including essential oils, completely water-soluble antioxidant material and known components which are both water-insoluble and organic solvent soluble, such as vitamin E and carnosic acid.
Yet another object of the invention is to provide a process for extraction of a water soluble antioxidant from natural plant materials which have had no contact with water-insoluble solvents and in which such solvents are not used in the extraction process and subsequently. Expressed in another way, it is regarded as an important object of the invention to provide such a process in which only plant materials and water, and optionally ethanol, are utilized to produce antioxidant material eminently suitable as an additive for human and animal consumption.
Other objects of the invention will become apparent from the description which follows.
It is believed that the present inventor is the first to recognize the presence of sodium rosmarinate in aqueous extracts from plant tissue of the Labiatae family and to isolate it therefrom. Accordingly, the present invention provides in one aspect, salts of the carboxylic function in rosmarinic acid, selected from a sodium salt isolated from tissue of plants of the Labiatae family, rosmarinic acid salts other than the sodium salt, or admixtures of said other salts with the sodium salt, which other salts or admixtures are those obtained by cation-exchange with said sodium salt from said tissue; an antioxidant material isolated by extraction from the tissue which is completely water-soluble and has a long shelf-life at ambient temperatures, and comprises the above-mentioned salt; and an aqueous solution which comprises such antioxidant material.
The antioxidant material of the invention, in powder form, has been found to have a shelf-life of at least two years at ambient temperatures.
A particular embodiment of the invention is constituted by a salt of the invention which has been chromatographically purified.